Fuel burning apparatus



y 5, 1958 A. SlFRlN ET AL 2,843,065

FUEL BURNING APPARATUS Filed April 21, 1952 2 Sheets-Sheet 1 INVENTORS flndreas Sifrzzz BY Otto Z062 m A W 'ATTORNEY July 15, 1958 A. SlFRlN ET AL 2,843,065

FUEL BURNING APPARATUS Filed April 21, 1952 2 Sheets-Sheet 2 FIG.2

INVENTORJ ndreas Jfrizz BY Otto lotz a'I MI/ ATTORNEY In IE6 FUEL BURNING APPARATU Andreas Sifrin and Otto Lotz, Oberhausen, Germany, as-

signors to The Babcock & Wilcox Company, New York, N. Y., a corporation of New Jersey Application April 21, 1952, Serial No. 283,292

9 Claims. (Cl. 110-28) The present invention relates to a fuel burning apparatus inwhich cyclone furnaces constitute the source of heat for an associated vapor generating unit. The cyclone furnaces are of the character disclosed in the copending application of Andreas Sifrin, Serial No. 202,981, filed December 27, E50, and now Patent No. 2,717,563, and thus are especially adapted for burning ash-containing solid fuels in a relatively coarsely pulverized or granular condition; the combustion being effected at furnace chamber temperatures above the ash fusion temperature to thereby maintain a discharge of incombustible ash residue from each cyclone furnace as liquid slag. More particularly, the cyclone furnaces embodied in the present invention are of a form in which the gaseous products of combustion are discharged from the combustion chamber adjacent the point of entry of the combustible mixture of fuel and air. Y

The granular fuels normally used in such furnaces have particle sizes of and under, and contain as a result of the fuel crushing operation a proportion of dustlike particles, known as fines. The fuel and air mixture is introduced in the combustion chamber through a tangential inlet arranged to effect a whirling motion of the fuel and air mixture in a helical path axially of and toward the opposite end of the furnace. In operation the entering fuel and air stream is rapidly ignited and the centrifugal effect of the whirling stream causes the ash particles released from the burning fuel particles to deposit in a molten condition on the furnace wall and form a film or layer of molten slag thereon on which the larger fuel particles are caught and burned.

In accordance with the present invention, several cyclone furnaces of the character hereinbefore described are arranged to discharge into a common heat receiving furnace because the size of .a single cyclone furnace is fixed, and its total range of operating capacity necessarily limited. The provision of several individually disconnectable cyclone furnaces therefore facilitates operation of the vapor generator at partial loads. Moreover, with cyclone furnaces of smaller diameter, a greater centrifugal effect is available than with cyclone furnaces of larger diameter for a given rate of fuel injection.

The usual cyclone furnace installation comprises a combination of furnace chambers which includes a primary cyclone furnace chamber, or a plurality of such chambers, in which the combustion of fuel is effected, a secondary chamber in a lower portion of the associated vapor generator, and arranged to receive the total discharge of gases from the cyclone chamber or chambers, and a radiant chamber into which gases from the secondary chamber are directed for transfer of heat to vapor generating elements contained therein. These chambers are so dimensioned as to size and cooling that at full load the slag is liquid in the cyclone combustion chamber or chambers, and in the secondary chamber, while the furnace gases in the radiantchamber have a temperature which is below the melting point of the slag. For this reason the slag is usually allowed to Patented July 15, 1958 drain from the primary cyclone chamber or chambers into the secondary furnace chamber and is tapped therefrom through a bottom opening. However, when operating at low partial loads, it may not be possible to maintain the entire secondary chamber at .a temperature which is above the melting point of the slag. As a result, the slag will not continue to drain from the secondary chamber when it strikes the bottom of that chamber at a point removed from the slag drain opening.

The foregoing difficulties can be eliminated by arranging the primary cyclone furnaces with their axes so steeply inclined to the horizontal that the discharging gaseous products of combustion are caused to impinge on the bottom of the secondary chamber. However, the slag will remain liquid mainly in the vicinity of the gaseous discharge and therefore, for each cyclone chamher there should be provided a slag drain opening in the bottom of the secondary chamber at a location toward which the gases from each particular furnace are directed. Such an arrangement may be avoided if, in accordance with the present invention, a slag drain opening is formed as a slot extending throughout the entire width of the secondary chamber parallel to the plane of the cyclone chamber axes with the bottom surface.

Cyclone furnaces arranged horizontally about parallel axes and discharging into a common secondary furnace chamber are known. In such forms, the plane of the cyclone axes is only slightly inclined downwardly toward the secondary chamber and the discharging gas streams are directed against an upright baffle wall and do not contact the bottom of the secondary chamber directly. In other known constructions, the cyclone furnaces are arranged about vertical axes, in which forms the gases are caused to strike the bottom of the secondary chamber, but at a locally limited point which is far removed from the slag drain opening and furthermore is arranged outside the secondary furnace chamber in the radiant chamber. With this last mentioned arrangement, the slag ahead of the slag drain opening tends to solidify when operating the furnace at partial load. Moreover, with the cyclone axis vertically arranged, it is diflicult to control the downward movement of fuel through the chamber because with tangential velocities too low, the fuel slides onto the cyclone furnace bottom in steep spirals. This condition is avoided if, according to the present invention, each cyclone furnace is arranged with its axis extending at a suitably steep inclination to the horizontal so that although the discharging gases are caused to impinge on the bottom of the secondary chamber, the angle of inclination is small enough to result in the centrifugal force being the dominating component of fuel movement through the cyclone furnace.

The slag outlet slot in the bottom of the secondary furnace is kept open most reliably when it lies within the sweep of the combustion gases. On the other hand, care must be taken that the larger quantity of slag entering from the cyclone furnaces is drained with certainty. This is best achieved if the slag outlet slot is positioned vertically below the slag outlet openings of the respective cyclone furnaces.

For partial load operation, however, the gas stream discharging from any one of the cyclone furnaces can sweep only that part of the secondary furnace bottom which lies in front of it. In order that the liquid slag will not yield laterally under the impact of the gases, and then solidify in its displaced position and thus form a kind of basin, the bottom of the secondary furnace is initially formed in such a manner that it provides, opposite each cyclone furnace, an open basin or trough to be longitudinally swept by gases from the corresponding cyclone furnace.

In order to cause the slag to be reliably discharged 6 fromthe secondary chamber at all points and at any load, there is arranged below the slag outlet slot a water tank, the connection of which is excluded from air and in which a scraping belt or the like is arranged parallel to the slag outlet slot.

At partial load, the furnace control is made especially difficult when the fuel is dried in the crusher or grinding apparatus by means of air or heating gases and when-the dust laden fumes are to be introduced in the combustion chamber without previous dust removal. According to this invention, therefore, these dust laden fumes are passed through a channel or duct which extends along the inside of a furnace boundary wall protected or formed by cooling tubes and the duct opens with individual openings at the lower end of the wall into the rising gas stream upon leaving the secondary furnace chamber or upon entering the radiant chamber.

For full load operation, as well as for operation at partial load, it is preferable to provide a secondary furnace chamber which is not too wide, but which is heated from two opposite sides. The chamber may be subdivided by a continuous or an interrupted central wall of cooling tubes. The best effect on the slag [low is achieved, however, when there is no central wall provided and the slag outlet slot lies in the center of the bottom of the secondary chamber.

With the axis of a cyclone furnace steeply inclined, and with air and fuel introduced tangentially adjacent the bottom outlet end, it is possible that with certain forms of furnaces, the fuel might not be lifted high enough by the entering air to reach the upper end of the combustion chamber. According to the present invention, therefore, the cyclone furnace is constructed so as to converge conically toward its top end. As a result of the decreasing cyclone chamber diameter in an upward direction, the rotating fuel-air mixture develops an increasing angular velocity suflicient to overcome the effect of gravity and thus continues to move in a helical path throughout the height of the chamber. In the course of such upward movement, the combustion of the fuel continues and a layer of slag is maintained on the circumferential wall areas. The lighter fuel particles are therefore burned in suspension, while the heavier fuel particles are caught and burned on the circumferential layer of slag. The entrainment of flying coke into the secondary chamber is thereby avoided. The axially outflowing gas stream will partly lose its rotational movement as it travels through the cyclone chamber so that it impinges against the bottom of the secondary furnace in the form of a solid stream.

A factor contributing to this result is the provision of a venturi-like form of gas outlet nozzle which prevents the formation of marginal disturbances.

If, in addition to the fuel-air mixture, secondary air is injected tangentially into the cyclone furnace, it is advisable to arrange the fuel-air jet in such a way that it is directed tangentially of the gas outlet nozzle. This provides the steepest angle at which the fuel-air jet can be injected against the tangent. For the purpose of maintaining this directional relationship, measures should be taken to avoid the agglomeration of coke in the vicinity of the fuel-air injection point, whereby the rotational movement of the stream would be disturbed.

The various features of novelty which characterize our invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating ad vantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which we have illustrated and described an embodiment of the invention.

Of the drawings:

.Fig. l is an elevational view, in symmetrical section, of a cyclone furnace unit constructed in accordance with the invention;

. Each half of the unit contains a group of three primary furnaces 1 of the cyclone type arranged in a row parallel to a side wall 2 of a secondary furnace 3. The cyclone furnaces 1 are mounted in inclined side wall arch portions 4 from which upper side wall portions 5 extend vertically. The walls of each cyclone furnace are constructed in known manner of cooling tubes, refractory material, insulation, and a sheet metal casing, all of which components are generally indicated. The walls of the secondary furnace are formed with wall cooling tubes 6 adjacent the inner faces thereof.

The cyclone furnaces 1 are disposed at an axial inclination of about fifty-five degrees to the horizontal and discharge almost perpendicularly against the refractory bottom 7 of the secondary furnace chamber 3. This refractory bottom 7 is formed with oppositely inclined sides 8, 8 toward which the discharge from the respective groups of cyclone furnaces is directed. The furnace bottom 7 is of zig-zag shape in the cross section, parallel to Walls 2, and thus provides successive pairs of oppositely inclined floor panels 9 which, at locations axially opposite each furnace 1, form a separate trough 10 which opens into a slag outlet slot 12 adjacent the corresponding furnace wall 2. A shaft 12a extends downwardly from each slot 12 into a water pool 13 which is maintained in a slag receiving tank 14 to a depth sufficient to provide a water seal preventing the escape of furnace gases despite the relatively high positive pressures prevailing in the secondary furnace chamber 3. The tank 14 has a scraping belt 15 submerged therein by which the granulated slag is discharged from the tank.

The furnace gases discharge axially from the respective cyclone furnaces 1 against the secondary furnace bottom 7 by which the gases are deflected and directed upwardly between the slag screen tubes 16 into the radiant chamber 17 of the vapor generating unit, of which only the lower portion is shown, the screen tubes 16 being formed as continuations of wall tubes 6 and extending upwardly from opposite inclined arch portions 4. Refractory channels or ducts 18 formed with nozzles 19' opening upwardly into the gas flow path are disposed adjacent the upper side walls 5 between wall tubes 6 and screen tubes 16 for the purpose of venting into the rising gases the dust laden fumes resulting from the air-drying of the granular fuel prior to delivery to primary furnaces 1. The addition of such fuel-bearing fumes at this point has the advantage that the temperature of gases in chamber 3 are not lowered whereas in passing to radiation chamber 17, beyond screen tubes 16, the temperature of the heating gases is advantageously increased.

Referring to Figs. 3 and 4, in particular, the combustion chamber of each cyclone furnace 1 includes a substantially cylindrical section 21 adjacent its inner gas outlet end formed by a circular wall 23, and a frustoconical section 21a adjacent its outer end formed by a correspondingly shaped circular wall 24 constituting a coaxial continuation of wall 23. At the inner end of each furnace 1 there is provided a concentric gas outlet 26, defined by a throat member or nozzle 27 of venturilike form extending normal to and through the combustion chamber inner end wall 28. The throat member 27 is of circular cross section throughout and of gradually increasing diameter and flow area toward opposite ends from a position of minimum flow area at approximately midway of its length. The throat member 27 is positioned in wall 28 so as to project from inner and outer sides thereof at approximately equal distances. As seen in section in Fig. 3, the inner surface 29 is symmetrically curved throughout in an axial direction, and the inner and outer edges 31, 32 are rounded. In the end Wall 28 of each cyclone furnace there is formed a slag outlet 33 which, in the operative position of the furnace, opens from the lowermost part of the furnace, as seen in Fig. 1. The walls 23, 24, 27 and 28 of the cyclone chamber and gas outlet nozzle are lined with refractory covered fluid conducting tubes 34-, 35, and 36, which are connected in suitable manner for continuous circulation of fluid therethrough, for example, in a common fluid circulation system with wall tubes 6 of the associated vapor generating unit.

Primary air-fuel conduits 41 are arranged to open into each cyclone chamber 1 through ports 42 arranged at diametrically opposite locations adjacent the inner end of throat member 27. As seen in Fig. 4, the inner ends of conduits 4-1 are bent so as to direct the fuel-air stream along paths tangent to the periphery of the gas outlet nozzle 2'7 at opposite sides. Conduits 43 are provided for introducing secondary air into each chamber ll through ports 45, also at diametrically opposite locations adjacent the inner end of nozzle 27 in a common transverse plane with air-fuel ports 42, but in a tangential direction relative to the inner circumferential wall of the chamber, the secondary air ports 45 being located down stream of the respective primary air-fuel admission ports 42. The outer flattened end 46 of each cyclone furnace 1 may be formed with a central bore 47, as indicated, through which air or oxygen may be admitted for burning fuel particles which may collect, for which purpose an openable closure, not shown, may be provided.

in the operation of each cyclone furnace 1, the combustible mixture of primary air and granular fuel is introduced through conduit 41 along a path which is tangent to the central gas outlet nozzle 27. Due to the slight deflection that the air-fuel stream undergoes at that location, the stream then impinges at a steep angle on the inner circumferential wall of the chamber where it is entrained by the stream of secondary air entering through conduit 43 along the same circumferential band. The fuel and air mixture burns in a whirling stream which follows a helical path along the inner circumferential wall and toward the upper end of the chamber. The greater portion of the incombustible ash residue from the burning fuel is deposited on the combustion chamber walls in molten condition and flows downwardly thereon in the outer layers, while the inner layers continue their rotational movement. As a result of the centrifugal force which increases with the curvature toward the outer end, the slag is forced downward in the conical section 21a and drains through opening 33 into the slag outlet shaft 12 for continuous disposal.

Due to the arrangement of the gas outlet throat 26, and the flow restrictive effect of the rearwardly tapering combustion chamber section 21a, the stream of gaseous products of combustion is caused to turn inwardly toward the central axis of the chamber for axial flow at increased velocity toward and through the gas outlet nozzle 26, and thence into the secondary furnace chamber 3. The nozzle 26 is so shaped as to prevent, on the one hand, freshly fed fuel being carried away immediately and, on the other hand, to intercept as far as possible those gases which may still be rotating and to direct them into the secondary chamber 3 without turbulence or expansion losses.

In the secondary chamber 3, the gases discharging from cyclone chambers l at opposite sides are directed at steep inclinations to the horizontal so as to impinge at angles of about 90 against the oppositely inclined sides 8 of the refractory bottom 7. Furthermore these gas streams impinge on inclined channel areas formed between successive oppositely inclined floor panels and thus maintain the deposited slag in continuous movement toward the discharge slots adjacent side walls of the furnace.

While in accordance with the provisions of the statutes we have illustrated and described herein the best form of the invention now known to us, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by our claims, and that certain features of the invention may sometimes be used to advantage without a corresponding use of other features.

We claim:

1. Apparatus for burning a slag-forming solid fuel comprising a plurality of oppositely arranged cyclone furnaces, each of substantially circular transverse crosssection about a vertically inclined longitudinal axis, means for introducing and burning a slag-forming solid fuel in each of said furnaces at a mean furnace temperature above the fuel ash fusion temperature, means forming a gas outlet arranged centrally of the lower end of each cyclone furnace, means forming a molten slag outlet in the lower end of each cyclone furnace separate from and at a lower level than the corresponding gas outlet, a secondary chamber having opposed upright walls with oppositely inclined arch sections at their upper ends through each of which the gas and slag outlets of a corresponding cyclone furnace are arranged to discharge separately, said secondary chamber having a heating gas outlet at its upper end between said oppositely inclined arch sections, and a floor for said secondary chamber having a central ridge portion from which opposite side portions slope downwardly towards said opposed upright walls and arranged so that the longitudinal axis of each cyclone furnace intersects an intermediate part of a corresponding floor side portion and so that the gases from the corresponding cyclone furnace gas outlet will sweep at least the upper part of the corresponding floor side portion before entering said secondary chamber heating gas outlet, said floor side portions terminating at their lower ends at points spaced from said opposed upright walls and each defining with the adjacent upright wall a slot arranged to receive molten slag discharging from said floor side portions and the corresponding cyclone furnace slag outlet.

2. Fuel burning apparatus as defined in claim 1 and further characterized by said floor side portions being formed in successive panels in a direction paralleling said opposing walls, each side portion including at least two successive panels arranged in downwardly converging relation and defining therebetween a slag drainage trough aligned with a cyclone chamber in one of said walls and discharging to one of said slag receiving slots.

3. Apparatus for burning slag-forming fuel which comprises a substantially cylindrical furnace chamber arranged with its axis vertically inclined and having a central gas outlet nozzle in a lower inclined end wall thereof, means for introducing a combustible mixture of air and slag-forrning fuel in suspension tangentially into the lower portion of said furnace chamber at a location inwardly adjacent said nozzle, means forming a conical extensionof said furnace chamber throughout a major portion of the height thereof from the inner end of said gas outlet nozzle, a slag outlet formed in said lower end wall below said gas outlet nozzle, said nozzle and said slag outlet opening into a common gas-and-slag receiving chamber from which the gases and slag are separately discharged, and means for directing secondary combustion air tangentially into said chamber at a location angularly displaced in a downstream direction from the location at which said combustible mixture is introduced.

4. Fuel burning apparatus as defined in claim 3 wherein said last named means is arranged to separately direct said secondary air into said chamber in a common circumferential band with said combustible mixture.

5. Fuel burning apparatus as defined in claim 4 wherein said gas outlet nozzle includes an annular inner end portion projecting inwardly of said furnace chamber from the inner side of said end wall, said means for introducing said combustible mixture into said chamber being arranged to direct said mixture tangentially of the periphery of said annular inner end portion of said nozzle.

6. Apparatus for burning a slag-forming solid fuel comprising a cyclone furnace of substantially circular transverse cross-section about a vertically inclined longitudinal axis, means for introducing and burning a slagforming solid fuel in said furnace at a mean furnace temperature above the fuel ash fusion temperature, means forming a gas outlet arranged centrally of the lower end of said cyclone furnace, means forming a molten slag outlet in the lower end of said cyclone furnace separate from and at a lower level than said gas outlet, a secondary chamber having an upright wall and an inclined arch section at its upper end through which said cyclone furnace gas and slag outlets are arranged to discharge separately, and an inclined floor in said secondary chamber sloping downwardly towards said upright wall and arranged so that the longitudinal axis of said cyclone furnace intersects an intermediate portion of said floor and the gases with slag particles in suspension from said gas outlet will sweep at least the upper portion of said inclined floor to deposit slag particles thereon and to maintain deposited slag particles in a molten condition, said floor terminating in a lower end portion spaced from said upright wall and defining therewith a slot arranged to receive molten slag discharging from said floor and said slag outlet.

7. Apparatus for burning a slag-forming solid fuel comprising a cyclone furnace of substantially circular transverse cross-section about a vertically inclined longitudinal axis, means for introducing and burning a slagforming solid fuel in said furnace at a mean furnace temperature above the fuel ash fusion temperature, means forming a gas outlet arranged centrally of the lower end of said cyclone furnace, means forming a molten slag outlet in the lower end of said cyclone furnace separate from and at a lower level than said gas outlet, a secondary chamber having an upright wall and an inclined arch section at its upper end through which said cyclone furnace gas and slag outlets are arranged to discharge separately, and an inclined floor in said secondary chamber sloping downwardly towards said upright wall and arranged so that the longitudinal axis of said cyclone furnace intersects an intermediate portion of said floor and the gases with slag particles in suspension from said gas outlet will sweep at least the upper portion of said inclined floor to deposit slag particles thereon and to maintain deposited slag particles in a molten condition, said floor having oppositely inclined upper surface portions defining a slag drainage channel in alignment with said cyclone furnace longitudinal axis and said floor terminating in a lower end portion spaced from said upright wall and defining therewith a slot arranged to receive molten slag discharging from said slag drainage channel and said slag outlet.

8. Apparatus for burning a slag-forming solid fuel comprising a cyclone furnace of substantially circular transverse cross-section about a vertically inclined longitudinai axis, means for introducing and burning a slagforrning solid fuel in said furnace at a mean furnace temperature above the fuel ash fusion temperature, means forming a gas outlet arranged centrally of the lower end of said cyclone furnace, means forming a molten slag outtet in the lower end of said cyclone furnace separate from and at a lower level than said gas outlet, a secondary chamber having an upright wall and an inclined arch section at its upper end through which said cyclone furnace gas and slag outlets are arranged to discharge separately, an inclined fioor in said secondary chamber sloping downwardly towards said upright wall and arranged so that the longitudinal axis of said cyclone furnace intersects an intermediate portion of said floor and the gases with slag particles in suspension from said gas outlet will sweep at least the upper portion of said inclined floor to deposit slag particles thereon and to maintain deposited slag particles in a molten condition, said floor terminating in a lower end portion spaced from said upright wall and defining therewith a slot arranged to receive molten slag discharging from said floor and said slag outlet, and means for sealing said slot against the intake of air into said secondary chamber.

9. Apparatus for burning a slag-forming solid fuel comprising a plurality of oppositely arranged cyclone furnaces, each of substantially circular transverse crosssection about a vertically inclined longitudinal axis, means for introducing and burning a slag-forming solid fuel in each of said furnaces at a mean furnace temperature above the fuel ash fusion temperature, means forming a gas outlet arranged centrally of the lower end of each cyclone furnace, means forming a molten slag outlet in the lower end of each cyclone furnace separate from and at a lower level than the corresponding gas outlet, a secondary chamber having opposed upright walls with oppositely inclined arch sections at their upper ends through each of which the gas and slag outlets of a corresponding cyclone furnace are arranged to discharge separately, said secondary chamber having a heating gas outlet at its upper end between said oppositely inclined arch sections, a floor for said secondary chamber having a central ridge portion from which opposite side portions slope downwardly towards said opposed upright walls and arranged so that the longitudinal axis of each cyclone furnace intersects an intermediate part of a corresponding floor side portion and so that the gases from the corresponding cyclone furnace gas outlet will sweep at least the upper part of the corresponding fioor side portion before entering said secondary chamber heating gas outlet, said floor side portions terminating at their lower ends at points spaced from said opposed upright walls and eacn defining with the adjacent upright wall a slot arranged to receive molten slag discharging from said floor side portion and the corresponding cyclone furnace slag outlet, tubes forming an inclined slag screen extending across said secondary chamber heating gas outlet, and means for burning a combustible mixture superjacent the lower portion of said slag screen.

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